Normal lymphocyte function is highly dependent on a variety of cell surface receptors that mediate cell-cell adhesion, and transmit contact-dependent activation signals to the cellular interior. The project described focuses on three adhesion-dependent responses in T and B cells. CD22 is a sialic acid-binding receptor that recognizes sIgM and CD45. This project will examine the role of sialylation of CD22 itself in the ligand-binding activity of this receptor. Wild-type and mutant forms of CD22 will be introduced into CD22 nullizygous B cells to determine whether alterations in the sialylation of the extracellular domain augments or interferes with the function of CD22. The investigator has identified a novel, inducible ligand for CD5 on activated B cells, and has shown that CD5 glycosylation regulates CD5 binding to this ligand. The investigator now plans to study the glycosylation of CD5 in detail, and to clone the novel CD5 ligand. Two cDNAs encoding putative ligands for the L-Selectin cytoplasmic domain have been cloned, and the objective of the third aim of this project is to characterize the cDNAs, and to examine their roles in L-Selectin-mediated adhesion and rolling.